Ground water at the Sutton Brook Disposal Area, a former municipal landfill in Tewksbury, Massachusetts, located adjacent to Sutton Brook, a tributary of the Shawsheen River, is contaminated by volatile organic compounds (VOCs). Results from the use of passive-vapor-diffusion samplers show vapor concentrations of petroleum hydrocarbons as high as 500,000 parts per billion by volume in pore waters of streambed sediments along an approximate 2,000-foot reach of Sutton Brook where it flows between lobes of the former landfill. Petroleum hydrocarbons were also detected in the sediments on the eastern shore of Quarry Pond, which is south of the southern landfill lobe, with a maximum vapor concentration near 2,000 parts per billion by volume. Vapor concentrations of petroleum hydrocarbons in the sediments of Sutton Brook vary by two to three orders-of-magitude over distances of 50 to 100 feet. Chlorinated hydrocarbons also were detected with passive-vapor-diffusion samplers, but generally at locations downstream of where petroleum hydrocarbons were detected, and mostly at vapor concentrations of less than 100 parts per billion by volume.